Two US airlines canceled a handful of flights to and from Mexico City’s international airport on Friday after the Popocatepetl volcano spewed a new column of ash, officials said.

United Airlines canceled its flights from and to Los Angeles and the Texas city of Houston, while AirTran scrapped one, an airport spokesman told AFP. Delta Airlines delayed some of its flights.

The new cancelations came one day after six US airlines called off 60 flights due to volcanic ash. Some 600 people waited for new flights home on Friday morning, the spokesman said.

In its latest bulletin, the National Disaster Prevention Center said the 5,452-meter (17,887-feet) high volcano had blown a 1.5 kilometer high column of ash that was heading west-northwest and produced low-intensity tremors in the last 24 hours.

Volcanic activity at the snow-capped Popocatepetl, located 65 kilometers (40 miles) southeast of the capital, has intensified since May, prompting authorities to raise the alert level to “yellow phase 3” for 27 days, just short of evacuation orders.